Error codes#

Mypy can optionally display an error code such as [attr-defined] after each error message. Error codes serve two purposes:

  1. It’s possible to silence specific error codes on a line using # type: ignore[code]. This way you won’t accidentally ignore other, potentially more serious errors.

  2. The error code can be used to find documentation about the error. The next two topics (Error codes enabled by default and Error codes for optional checks) document the various error codes mypy can report.

Most error codes are shared between multiple related error messages. Error codes may change in future mypy releases.

Displaying error codes#

Error codes are displayed by default. Use --hide-error-codes or config hide_error_codes = True to hide error codes. Error codes are shown inside square brackets:

$ mypy prog.py
prog.py:1: error: "str" has no attribute "trim"  [attr-defined]

It’s also possible to require error codes for type: ignore comments. See ignore-without-code for more information.

Silencing errors based on error codes#

You can use a special comment # type: ignore[code, ...] to only ignore errors with a specific error code (or codes) on a particular line. This can be used even if you have not configured mypy to show error codes. Currently it’s only possible to disable arbitrary error codes on individual lines using this comment.

You can also use --disable-error-code to disable specific error codes globally.

This example shows how to ignore an error about an imported name mypy thinks is undefined:

# 'foo' is defined in 'foolib', even though mypy can't see the
# definition.
from foolib import foo  # type: ignore[attr-defined]

Enabling specific error codes#

There are command-line flags and config file settings for enabling certain optional error codes, such as --disallow-untyped-defs, which enables the no-untyped-def error code.

You can use --enable-error-code to enable specific error codes that don’t have a dedicated command-line flag or config file setting.

Per-module enabling/disabling error codes#

You can use configuration file sections to enable or disable specific error codes only in some modules. For example, this mypy.ini config will enable non-annotated empty containers in tests, while keeping other parts of code checked in strict mode:

[mypy]
strict = True

[mypy-tests.*]
allow_untyped_defs = True
allow_untyped_calls = True
disable_error_code = var-annotated, has-type

Note that per-module enabling/disabling acts as override over the global options. So that you don’t need to repeat the error code lists for each module if you have them in global config section. For example:

[mypy]
enable_error_code = truthy-bool, ignore-without-code, unused-awaitable

[mypy-extensions.*]
disable_error_code = unused-awaitable

The above config will allow unused awaitables in extension modules, but will still keep the other two error codes enabled. The overall logic is following:

  • Command line and/or config main section set global error codes

  • Individual config sections adjust them per glob/module

  • Inline # mypy: ... comments can further adjust them for a specific module

So one can e.g. enable some code globally, disable it for all tests in the corresponding config section, and then re-enable it with an inline comment in some specific test.